Solvent disperser for removing oil from sponge core

ABSTRACT

In a solvent extraction process for removing captured formation fluids from sponge core, a sintered metal plate solvent disperser directs returned solvent, in the extractor, outwardly onto the sponge in a sponge core cylinder.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to copending U.S. patent application Ser. No. 814,334,filed Dec. 27, 1985, the disclosure of which is incorporated herein byreference, and to U.S. patent application Ser. No. 035,111, filedcontemporaneously herewith (Docket T-8226), both of which are assignedto the assignee of the present application.

BACKGROUND OF THE INVENTION

The present invention relates to the exploration and production ofpetroleum from earth formations, and more particularly to methods fordetermining the amount of oil present in such a formation.

In the petroleum industry, one of the most valuable and informativetechniques for determining the characteristics of an earth formationlocated well below the surface, and the nature of the fluids which itmay contain, is to remove and bring a portion of the formation to thesurface for analysis. This is most commonly done by "coring" theformation. Of course, physical conditions in the formation aresubstantially different from those at the surface: pressures andtemperatures are ordinarily enormously elevated over surface conditions.Therefore, fluids and gases present in porous rock samples very oftenevolve from those samples as they are recovered from the formation. Tothe extent that such liquids and gases are lost, the accuracy of theevaluation of the formation production potential is accordinglyimpaired.

To control this problem, a technique called "pressure coring" is oftenemployed. With pressure coring, the core is contained at substantiallyits original formation pressure until proper analysis can be made.Pressure coring, while overcoming fluid loss problems to a great extent,is quite expensive.

A recently developed alternative technique, "sponge coring", showstypical savings of around 70 percent of the cost of pressure coringafter considering the savings in both the cutting of the core from theformation and the subsequent analysis of the core. In sponge coring, asthe core is cut, it enters a typically half-inch thick polyurethanesponge liner inside the inner core barrel. As the core is brought to thesurface, the sponge then captures any formation fluids that escape fromthe core when the pore pressure drops below the oil's bubble point. Suchexpanding gas bubbles can displace otherwise immobile oil, and any suchoil which bleeds from the core (and this can be as much as 50% of theoriginal core fluid) is thus caught and retained by the sponge liner. Ananalysis is then made of the oil captured by the sponge, and by addingthat to the amount left in the core, one can obtain much more accurateoil saturation values for the formation from which the core was removed.

The importance of coring in the production of petroleum has recentlybeen increasing as more and more secondary and tertiary recovery isbeing made of petroleum reserves. In a formation undergoing primaryproduction, the original reservoir fluids are little altered from theirconditions for the last several thousand years. They may migrate as theoil is produced, but their properties are little changed. However, whenfluids and/or other compounds are injected into a formation to stimulateits production, the nature of the connate fluids is accordingly altered,sometimes to a very substantial extent. When this occurs, the moretraditional wellbore logging tools may be unable to provide furtheruseful information. In all too many instances, the only way to determinehow much oil is left, and thus whether it can be produced economically,is to go down to the formation and take a core sample.

It will therefore be appreciated that the analysis of the oil content ofthe core sample can be critically important. The final true residual oilsaturation of a formation is a determination that can make or break amulti-million dollar enhanced recovery project.

As explained in greater detail in the above-referenced '334 application,a major disadvantage of sponge coring has been the inability toaccurately measure the amount of oil retained by the sponge. Manytechniques for oil determination have been used by service companies,including mechanical extraction, retorting, and solvent extraction. Theproblems with these techniques, as they are presently practiced, includeincomplete extraction of oil, mistaking extracted sponge components foroil, and in the case of solvent extraction, incomplete removal ofextracting solvent before measuring oil volume.

The above-referenced '334 application discloses a substantialimprovement in determining the amount of oil in a sponge core. Severalsolvents are identified which have the unique capacity, previouslyunrecognized in this industry, to remove substantially all of the oilcaptured by the sponge without affecting the sponge or dissolving(usually unreacted) sponge components. Highly accurate determination ofthe oil captured in the sponge is thus made possible, therebyeffectively realizing the enormous savings potential of sponge coretechnology.

There does remain a need, however, to be able to practice thissubstantial improvement in an efficient and commercially practicalmanner such that substantial quantities of sponge core (often severalhundred feet of core in a typical coring operation) can be analyzedquickly and efficiently. For example, when sponge core is manufactured,the sponge is foamed in place inside an aluminum liner. The sponge thenbonds fairly well to the aluminum, making removal of the sponge from theliner difficult and time consuming. In analyzing the sponge core, itwould therefore be preferably to analyze it in place in the linerbarrel.

A need thus remains for a convenient, effective, and comerciallypractical method and apparatus for removing the captured oil from thesponge, preferably without having to remove the sponge from the aluminumliner. A need also remains for a method for accurately analyzing theactual amount of oil removed when solvents such as the Freon-11identified in the above-referenced '334 application are used. Typically,a large amount of solvent is used, resulting in a highly dilutedsolution, since there is usually not much oil present. Removing thesolvent in order to improve the accuracy of the determination of the oilis not as easy as simply evaporating the solvent because the light(e.g., C₅ -C₈) hydrocarbons from the captured formation oil will usuallyalso evaporate.

SUMMARY OF THE INVENTION

Briefly, the present invention meets the above needs and purposes byproviding a large size solvent extraction device in which lengths of thealuminum liner (typically one foot) with sponge intact therein can beplaced for solvent extraction. A unique solvent disperser assures thatthe solvent will be distributed and applied to the sponge. After the oilhas been removed from the sponge, a unique distillation method andanalytical procedure are provided which accurately determine the volumeof oil removed from the sponge, including the light hydrocarbons.

More particularly, large Soxhlet extractors are furnished in whichone-foot sections of the aluminum liner, with sponge intact therein, arelocated. The solvent is refluxed in conventional manner through theSoxhlet extractor. However, the refluxed solvent in such an extractorordinarily drips down the center and would miss the sponge, since thesponge core lines the inner wall of the aluminum cylinder and is hollowin the center. Therefore, to prevent the solvent from merely drippingdown the hollow center of the cylinder without contacting the sponge,the present invention provides a unique solvent disperser especiallyadapted for use in determining the oil captured by the sponge core.

In particular, the disperser includes a body which is capable ofconducting liquid solvent therein, e.g., by capillary and/orgravitational action. The body includes a region, defining anapplication zone, which matches the dimensions of the sponge forconducting solvent to the sponge and passing it to the sponge. Thesolvent disperser body also includes a region for receiving solventwhich is dripping downwardly within the Soxhlet extractor and dispersingthe solvent by conducting it to the application zone, whence it isdelivered to the sponge.

Once the oil has been removed from the sponge, it is then analyzed byfirst distilling but a portion of the solvent from the solvent/oilmixture. Thus, in such a solvent extracted sponge core measurementprocess, the solvent/oil mixture is first separated from the water inthe extracted fluids. Next, the mixture is carefully distilled to removea portion of the solvent from the solvent/oil mixture substantiallywithout co-distillation or loss of the light hydrocarbons in themixture. Typically, with Freon-11 solvent, the solvent can be removeduntil the remaining solution contains less than 15% Freon-11, withoutsignificant loss or co-distillation of the light hydrocarbons. Adetermination of the solvent remaining in the mixture is then made,following which the actual volume of oil removed from the sponge is thendetermined by subtracting the determined remaining solvent volume.

In a preferred embodiment of the invention the disperser is a discshaped capillary body made from a sheet of sintered stainless steel andhaving several vents formed therein for permitting vapor to passtherethrough. The capillaries in the sintered stainless steel bodydefine solvent conduits for conducting solvent liquid within the body.On the outward rim of the body is an application zone which isdimensioned for contacting the sponge in a sponge core barrel forreceiving solvent from the capillary conducting means within thesintered stainless steel body and passing the solvent to the sponge. Theunderside of the body outside the application zone has a burnishedsurface in order to substantially close the pores of the underside ofthe body to help retain solvent within those portions of the body whichare distant from the sponge. In the center of the body is a raised hubfor receiving the solvent dripping down from the extractor anddispersing the solvent outwardly to the application zone, the hub beingraised and located above the rest of the body to gravitationally assistthe solvent in flowing away therefrom.

In the preferred embodiment of the invention, Freon-11 solvent is usedfor extracting the oil from the sponge core. The preferred method forquantifying the volume of oil in the fluids resulting from suchextraction then proceeds by first separating the solvent/oil mixturefrom the water in the extracted fluids. Next, a Vigoreaux fractionaldistillation reflux column surmounted with a column condenser is thenemployed to distill at least a portion of the solvent from thesolvent/oil mixture. With this method, the solvent portion is distilledwithout substantial co-distillation or loss of the light C₅ -C₈hydrocarbons in the mixture. This is accomplished by graduallydistilling until a vapor temperature limit of substantially 65° Celsiusis reached in the solvent/oil mixture. At that point, distillation isdiscontinued.

Even though the Freon-11 solvent removes very little of the polyurethanesponge core material, there will nevertheless be some extracted spongecomponents in the resulting solvent/oil mixture. This is believed to bedue in large part to chemical degradation of the sponge resulting fromprior exposure to borehole conditions such as elevated temperatures,hydrogen sulfide, and the solvent action of the formation fluidsthemselves. These extracted sponge components are then removed from thesolvent/oil mixture by centrifugation. Next, the amount of solventremaining in the mixture is determined utilizing gas chromatography, andthe volume of oil actually removed from the sponge is then finallydetermined by subtracting from the volume of the mixture the volume ofthe solvent which was thus determined. Typically, the volume of Freon-11remaining will be less than 15%.

It is therefore an object of the present invention to provide asubstantially improved method and apparatus for determining the amountof oil in sponge core; such a method and apparatus in which the oil canbe removed from the sponge while the sponge may be left intact in thesponge core barrel; in which a solvent disperser is employed having abody including solvent conducting means for conducting solvent withinthe body; in which the body has an application zone located anddimensioned for receiving solvent from the solvent conducting means andpassing such solvent to the sponge in a sponge core barrel; in which thesolvent conducting means includes means for receiving solvent drippingdownwardly onto the body and dispersing such solvent to the applicationzone; and to accomplish the above objects and purposes in aninexpensive, uncomplicated, versatile, economical and reliable methodand apparatus readily suited to the widest possible utilization in theanalysis of oil-bearing earth formations by sponge coring methods.

These and other objects and advantages of the invention will be apparentfrom the following description, the accompanying drawings, and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary cross-sectional view of a Soxhlet extrationapparatus and system for solvent removal of the oil from the spongecore;

FIG. 2 is a plan view of the disperser employed in the system shown inFIG. 1;

FIG. 3 is a cross-sectional view of the disperser shown in FIG. 2, takenon line 3--3 thereof;

FIG. 4 is a bottom view of the disperser taken on view line 4--4 in FIG.3;

FIG. 5 is a fragmentary partially sectioned view of the solventextraction apparatus and system for removing most of the solvent fromthe solvent/oil mixture;

FIG. 6 is a cross-sectional view of a measuring tube used for measuringthe final volume of the concentrated solvent/oil mixture; and

FIG. 7 is a flow chart illustrating the steps performed in quantitationof the oil in the sponge core solvent/oil extracts.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings, the new and improved method andapparatus for use in determining the oil saturation of an earthformation by means of sponge coring will be described. The sponge coreand liner are left intact, and cut into lengths of convenient size, suchas one-foot sections 10 (FIG. 1). The section 10 then consists of thealuminum barrel 11 and the polyurethane sponge 12 lining the insidethereof. The center of the section 10, as can be seen, is hollow, havingpreviously received the formation core sample therein.

The section is then placed in an oversized Soxhlet extractor 15 ofsufficient size to receive a section 10. The solvent 16 in the bottom ofthe extractor 15 is heated at the bottom by a heater 17 causing solventvapors to rise and be condensed in an Allihn condenser 18, cooled bycoolant 19. The solvent then drips back down so that it can percolatethrough the sponge for removing the formation fluids therefrom. In thepreferred embodiment, the reflux rate of the solvent was equal toapproximately one to two times the pore volume of the sponge per hour,and the process was continued for approximately 48 hours. Due to the lowboiling point of the Freon-11 solvent (23.8° C., the coolant 19 isrefrigerated, preferably around ice-water temperatures (e.g., using awater-ethylene glycol coolant at 3° C.).

In order to assure proper dispersion of the recirculating solvent 16,which drips down through the center of the Soxhlet extractor 15 from thecondenser 18, a solvent disperser 25 is located on top of theliner/sponge section 10. Disperser 25, in the preferred embodiment, is adisc shaped capillary body made from a sheet of sintered stainlesssteel. Formed in the shape of a spoked wheel, the disperser 25 has acentral hub 27 from which a series of spokes 28 radiate to an outer rim30. The openings 31 between the rim and spokes provide vents 31 for thesolvent vapor to rise to the condenser 18. The sintered stainless steelis thus a porous capillary body which readily conducts the solvent as itdrips downwardly onto the hub 27. As can be seen from the drawings, thehub 27 is raised and located above the rest of the disperser body 25 sothat the flow of the solvent away from hub 27 is further assisted bygravity.

The bottom of the rim 30 constitutes an applicaton zone 33 which, as canbe seen, is dimensioned for contacting the sponge 12 in the sponge corebarrel 11. The rim 30 thus receives solvent from the capillaries withinthe disperser 25 and passes the solvent on to the sponge 12.

The underside of the hub 27 and spokes 28 of disperser 25 is burnishedto close the pores of the disperser body 25 on the underside thereof inthose areas outside the application zone 33 on the underside of the rim30. This discourages the solvent from dripping off the disperser 25outside the application zone, thus helping to retain solvent withinthose portions of the disperser body 25 which are distant from thesponge 12.

At this point, the fluid mixture is highly diluted with solvent. Inorder to accurately quantify the extracted volume of oil, it istherefore desirable to remove the solvent therefrom. According to thepreferred embodiment of the invention, it has been discovered that it ispreferable, in order to retain the light hydrocarbons, not to remove allof the solvent. Rather, the majority of the solvent is removed and thenthe volume of the remaining solvent is determined.

To accomplish this, the solvent extraction apparatus 40 illustrated inFIG. 5 was employed, consisting of a 100 ml round bottom flask 45,Vigoreaux fractional distillation column 47, and a condenser assembly49. The distillation column 47, operating at ambient room temperature,thus provides a dynamic separation of the solvent from the solvent/oilmixture 50. By employing active distillation in this fashion, ratherthan simply trying to evaporate the solvent from the mixture, loss ofthe light hydrocarbons from the mixture 50 is effectively curtailed.

Prior to introducing the solvent/oil mixture 50 into the flask 45, it isplaced in a separatory funnel 52, where the water 54 is allowed to riseabove the solvent/oil mixture. In this way, the water in the extractedfluids is separated from the solvent/oil mixture before introductioninto the flask 45. As space then becomes available within flask 45,during distillation (aided by heater 55), additional amounts of thesolvent/oil mixture are introduced, over time, from the separatoryfunnel 52, until all of the solvent/oil mixture is in the flask 45.Distillation of the mixture in flask 45 proceeds, in the preferredembodiment, until the vapor temperature reaches approximately 65° C., atwhich time heating is discontinued and the mixture is allowed to cool.Typically, the solvent/oil mixture in flask 50 can be concentrated,without significant loss of light ends, by distillation, until theremaining solution contains less than 15% Freon-11. The distilledFreon-11 is collected in flask 57. Temperatures may be convenientlymonitored by thermometers 61 and 62.

Next, the concentrated solvent/oil mixture is centrifuged in acentrifuge tube 64 to separate and remove the extracted spongecomponents 65 from the solvent/oil mixture 50, and the residual Freon inthe solvent/oil mixture is measured by standard gas chromatography (notshown). From these measurements the volume contribution of the solventremaining in the mixture is readily determined, and can be subtracted,thereby yielding the volume of the oil actually removed from the sponge.These measurements can be conveniently made using a centrifuge tube 64having a volume calibration scale on the side thereof, and by adding aquantity of water 67 sufficient to more visibly separate the spongematerial 65 from the solvent/oil mixture. Water will usually have anintermediate density, or a base can be added to adjust the density asappropriate.

In measuring the residual solvent by gas chromatography, standardprocedures are followed, in which oil-solvent standard solutions on avolume-to-volume basis are used. Due to the high volatility of theFreon-11 used in the preferred embodiment, it has been considered moreaccurate to prepare the standard solutions on a weight-to-weight basisand then convert them to a volume-to-volume basis. This was done byinjecting a known weight of Freon into a vial sealed with a mininertvalve containing the known weight of oil. The type of standard thusobtained is a weight-to-weight ratio. Conversion to a volume-to-volumeratio is done by a determination of the densities of the Freon and oil.The respective component volumes are then calculated for avolume-to-volume standard to be consistent with the use of constantvolume aliquots of unknowns.

As may be seen, therefore, the present invention has numerousadvantages. Principally, it provides a very convenient, efficient, andcost effective method and apparatus for accurately determining the oilsaturation of an earth formation by means of sponge coring. The spongecan be left intact in the metal barrel in which it is usually formed andto which it is usually tightly adhered. The solvent is efficientlyrefluxed through the sponge for extracting all of the oil from thesponge. The volume of oil removed from the sponge is then accuratelydetermined with little if any loss of the light hydrocarbons therefrom.The technique is robust, yielding consistent results over very wideranges, such as, for example, 19°-43° gravity oil. The invention is thushighly versatile, efficient, accurate, reliable, and readily suited tothe widest utilization in the analysis of oil-bearing earth formationsby sponge coring methods.

While the methods and apparatus herein described constitute preferredembodiments of this invention, it is to be understood that the inventionis not limited to these precise methods and apparatus, and that changesmay be made therein without departing from the scope of the invention.

What is claimed is:
 1. A solvent disperser for use in determining theoil saturation of an earth formation by means of sponge coring,comprising:(a) a body, (b) means in said body defining solventconducting means for conducting solvent liquid within said body, (c)said body including means defining an application zone located anddimensioned for receiving solvent from said solvent conducting means andpassing such solvent to the sponge in a sponge core barrel, and (d) saidsolvent conducting means including means for receiving solvent drippingdownwardly onto said body and dispersing such solvent to saidapplication zone.
 2. The apparatus of claim 1 wherein said body furthercomprises a disc.
 3. The apparatus of claim 1 wherein said body ismetallic.
 4. The apparatus of claim 1 wherein said body is made ofsintered metallic material.
 5. The apparatus of claim 4 wherein saidbody further comprises means substantially closing the pores of saidbody on the underside thereof substantially outside said applicationzone, to help retain solvent within those portions of said body whichare distant from such sponge.
 6. The apparatus of claim 5 wherein saidmeans substantially closing the pores of said body further comprisesmeans forming a burnished surface thereon.
 7. The apparatus of claim 1wherein said body further comprises a disc made from a sheet of sinteredstainless steel.
 8. The apparatus of claim 1 further comprising means insaid body for permitting vapor to pass therethrough.
 9. The apparatus ofclaim 8 wherein said means in said body for permitting vapor to passtherethrough further comprises means forming at least one vent throughsaid body.
 10. The apparatus of claim 1 wherein said means for receivingsolvent further comprises a hub on said body.
 11. The apparatus of claim10 wherein said hub is located substantially in the center of said body.12. The apparatus of claim 10 wherein said hub is a raised hub locatedabove the rest of said body to gravitationally assist such solvent inflowing away therefrom.
 13. A solvent disperser for use in determiningthe oil saturation of an earth formation by means of sponge coring,comprising:(a) a disc shaped capillary body made from a sheet ofsintered stainless steel, (b) means forming at least one vent throughsaid capillary body for permitting vapor to pass therethrough, (c) thecapillaries in said body defining solvent conducting means forconducting solvent liquid within said body, (d) said capillary bodyincluding means defining an application zone located outwardly on saidbody and dimensioned for contacting the sponge in a sponge core barrelfor receiving solvent from said solvent conducting means and passingsuch solvent to such sponge, (e) means on said body forming a burnishedsurface substantially closing the pores of said body on the undersidethereof substantially outside said application zone, to help retainsolvent within those portions of said body which are distant from suchsponge, (f) said solvent conducting means including a hub locatedsubstantially in the center of said body for receiving solvent drippingdownwardly onto said capillary body and dispersing such solventoutwardly to said application zone, said hub being raised and locatedabove the rest of said body to gravitationally assist such solvent inflowing away therefrom.
 14. A method for dispersing solvent for use indetermining the oil saturation of an earth formation by means of spongecoring, comprising:(a) receiving solvent dripping downwardly, and (b)conducting the received solvent by means of capillary action to anapplication zone located and dimensioned for passing such solvent to thesponge in a sponge core barrel.
 15. The method of claim 14 wherein saidstep of conducting the received solvent to an application zone furthercomprises conducting the received solvent by means of both capillary andgravitational action.